The World Health Organization is shaped by its members: 194 countries that set health priorities and make agreements about how to share critical data, treatments, and vaccines during international emergencies.

Public health experts say the United States’ departure could cripple the WHO’s operations or leave an opening for China to assume greater control over the agency.

Public health experts say U.S. withdrawal from the W.H.O. would undermine the nation’s standing as a global health leader and make it harder to fight the next pandemic.